FIELD OF THE INVENTION
The invention relates to a system for removing waste byproducts of aquatic life maintained in a closed water system. And in addition, this invention relates to a system for removing contaminants other than those directly related or generated by aquatic life.
Ammonia is the main byproduct of protein metabolism excreted by most aquatic animals and, unless removed efficiently and continuously, it will make life in an aquarium unsupportable.
Ammonia rapidly attains toxic concentrations in the confines of an aquarium. It exists as a mixture of free ammonia (NH.sub.3) and ionized ammonia (NH.sub.4, ammonium) in equilibrium. This does not mean that they are present in equal proportion, but that they are converted from one to the other at an equal rate. Free ammonia is uncharged and is a gas dissolved in water. It can pass unimpeded through membranes such as fish gills. This allows it to interfere with the normal excretion of ammonia and is believed to account for its toxicity. Ionized ammonia is a charged particle and does not exist as a gas. It cannot pass through membranes and it is therefore considered to be relatively nontoxic. Ammonia can be removed from an aquarium by depleting either free or ionized ammonia. Since it is in equilibrium, removing either component will ultimately remove both components.
Prior art configurations use ion exchangers to remove ionized ammonia, but only in fresh water. The presence of even low concentrations of salts in fresh water interferes significantly with ammonia removal by ion exchange. The most prevalent material used for this is zeolite, a natural mineral, more commonly known as cat litter.
One of the most conventionally utilized prior art processes uses the classical reaction of ammonia with formaldehyde to form methenamine as the ammonia removal.
Another prior art approach is biofiltration, an effective mode for removing ammonia, nitrites, and nitrates from marine or freshwater aquariums. In those systems, the water is percolated through a filter or reactor containing appropriate bacteria on a carrier or support. Some genera of anaerobic bacteria that utilize lactate may also be used to reduce nitrates, but that approach has shortcomings.
Three genera of bacteria, omnipresent in the environment, can usually establish themselves in the aquarium environment and metabolize the inorganic nitrogen compounds that would otherwise accumulate there: Nitrosomonas, Nitrobacter, and Thiobacillus. Nitrosomonas convert aquarium ammonia to nitrite, which Nitrobacter convert to nitrate, which Thiobacillus anaerobically convert to nitrogen gas.
Nitrosomonas are short gram-negative rods of about 0.8 by 1.5 u. They are obligate chemolithotrops, strictly aerobic, that convert ammonium to nitrite. Nitrobacter are also short gram-negative rods, about 0.7 by 1.5 u, strictly aerobic, obligate chemolithotrops, that convert nitrite to nitrate. Thiobacillus are short gram-negative rods, about 0.5 by 2 u, strictly autotropic and facultatively anaerobic. They require reduced sulfur compounds as an energy source, converting them to sulfate, using nitrate as an electron acceptor to form nitrogen gas. Carbon dioxide is their only source of carbon. In the presence of oxygen they utilize ammonia.
One of the problems associated with a biological system is that excessive dissolved organics are inhibitors to all these genera.
While the afore-mentioned bacteria can exist as free swimming agents, they do much better on a support matrix. A vast number of different configurations have been known heretofore, with each new generation touted as the best supporting structure for the bacteria to proliferate on, and providing information on how the supporting structure should be placed in any given system. Both Nitrobacter and Nitrosomonas require oxygen.
For that reason, aeration and circulation are essential. The prior art has endeavored to maximize oxygen levels in the aquarium to accommodate these genera. Both genera are intolerant of free ammonia and this can be the main cause of difficulties in getting an aquarium to cycle. "Cycle", in this context, is defined as successfully establishing the above-mentioned genera of bacteria.
For that reason, the art recommends that animals or ammonia should be introduced gradually to avoid sharp increases in ammonia concentration in this system.
Effective use of Thiobacillus requires anaerobic conditions (no oxygen). This can be achieved by passing the water slowly enough through special substrate so there is sufficient oxygen depletion from the water. Thiobacillus must also have a continuous supply of reduced sulfur compounds such as thiosulfate, or bisulfite.
An alternative prior art method of removing nitrates is the promotion of vigorous algae growth, either by harvesting algae in the aquarium itself or in a separate algae filter. This usually requires vitamin and trace element supplements as well as intense lighting.
The art distinguishes three types of filtration: mechanical, biological, and chemical. Mechanical filtration has to do with the (mechanical) removal of insoluble particulates from the water by some sort of sieving device, such as floss or foam. Biological filtration is the removal of ammonia and nitrite waste from the water by Nitrosomonas and Nitrobacter bacteria, respectively, and is the most essential of the filtration types used in the aquarium art. Chemical filtration is the direct removal of solutes by adsorption. The most important function of the chemical filtration is the removal of organic waste. This is vital because organic waste is both inhibitory to the biological filter and increases the load on the biological filter. The most common chemical adsorbent is activated carbon. Other types of chemical filtration include synthetic adsorbents, ion exchangers, and zeolite. In marine water, ion exchangers can remove some nitrite and nitrate, but have no significant effect on ammonia.
The marine aquarium environment is relatively well defined. The principal factors that need to be managed are pH, alkalinity, ionic integrity, trace element supplementation, stress, temperature, and the avoidance of chlorine, chloramine, and excessive phosphates.
Fundamental to the success of a healthy aquarium no matter what size, is the stability of the aquarium environment. The prior art relies on scheduled methodical water changes to remove wastes not normally removed by present filtration methods. Prior art also relies on water changes to restore the aquarium to a balanced ionic condition. No system exists today that is fully successful in the removal of organic waste and other contaminants in aquariums, other than water changes. However, unless large proportions of the aquarium water are exchanged during a water change or very frequent water changes are performed, the effect of the dilution of organic wastes and an improvement of ionic conditions are insignificant and insufficient.
Shortcomings of the prior art methods can be best shown by way of an exemplary situation: Nitrate (NO.sub.3) is presumed to be the unwanted substance. While in a realistic situation there are always more than just one substance to be eliminated from the closed aquarium system, we will, for the purpose of this example, only concentrate on nitrate. The aquarium water quality is tested by means of a test kit for pH, alkalinity, ammonia, nitrite, nitrate, oxygen, hardness, etc. By combining the results of these tests with a few mathematical calculations, one can come to a conclusion on how to rectify poor conditions.
We will assume a 100 gallon aquarium fully stocked with fish and invertebrates and a fully functioning filtration system.
A nitrate reading is taken at 100 mg/L of NO.sub.3. A partial water change of no more then 25% per month is recommended by one manufacturer of synthetic salt (other manufacturers recommend to exchange no more than 10% to 20% at any one time). After a 25% water change is completed, a new reading of 75 mg/L NO3 is recorded. That is a 25% improvement. Next month a nitrate reading is taken at 125 mg/L NO3, which is a normal result because there is still a constant input of NO.sub.3 into the aquarium. Another 25% water change is completed and the new reading is 93.75 mg/L NO.sub.3, only 6% better than the first water change with a NO.sub.3 reading of 100 mg/L. The third month nitrate is checked and it is 143.75 mg/L NO.sub.3. A partial water change of 25% is performed and the new reading is 107.8 mg/L NO.sub.3. After only three months, water changes have shown to be ineffective in lowering the nitrate content in the aquarium to an acceptable level.
Various options are available. The number of fish in the aquarium could be reduced. The frequency of the water changes past the recommended amount of 25% per month could be increased. Or, maybe the fish and invertebrates could be subjected to increasingly poor water conditions and hope for the best. Nitrates were chosen for this example because of their difficulty to be removed in prior art systems.
Nitrates do not rise and fall precipitously, and nitrate content can be used as a barometer of overall water quality. The chemistries of nitrates and marine water are such that the removal of nitrates from sea water by either physical or chemical processes is very ineffective. As noted above, prior art methods rely on the removal of nitrates by anaerobic denitrification or the harvesting of vegetative growth to supplement water changes as the means of controlling nitrates. Hobbyists and professional maintenance personnel of public aquaria have kept fish in high nitrate water (over 100 mg/L nitrate) for years with no perceptible ill effects on fish and many invertebrates. However, low nitrate concentrations become important when the objective is the maintenance and growth of delicate corals in reef systems. Low nitrates also help control the proliferation of hair algae.
Nitrate is only one of the many elements not wanted in the aquarium water. Phosphate, excessive organics, nitrite, ammonia, and chloramines are some others. Phosphate, is a major nutrient requirement for micro-algae, along with nitrate and some trace elements. Therefore the removal of phosphate is beneficial to a marine aquarium. If one could, so to speak, dial in on exactly what one wants removed and what one wants to stay, without having a separate apparatus for each element, such a device would be truly revolutionary in the art of maintaining a closed water system such as an aquarium.